1. Field of the Invention
This invention relates to a machining tool, more particularly to an apparatus for driving a cutter holder in a machining tool.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional apparatus for driving a cutter holder in a numerical control machining tool is shown to include a sleeve 11, a holder carrying rod 12, a cutter holder 13, a cylinder body unit 14, and a piston rod 15. The sleeve 11 and the cylinder body unit 14 are adapted to be disposed on a machine bed 10. The holder carrying rod 12 is journalled on a bearing unit 111 in the sleeve 11, and is biased by a spring unit 112 to move toward a front end of the piston rod 15. Accordingly, the holder carrying rod 12 can reciprocate in the sleeve 11. When the cutter holder 13 moves in the sleeve 11 rearward toward the cylinder body unit 14, it holds a cutter (not shown) thereon. When the cutter holder 13 moves in the sleeve 11 forward away from the cylinder body unit 14, it releases the cutter (not shown) therefrom. When the piston rod 15 moves forward in the cylinder body unit 14 to contact the holder carrying rod 12, a forward thrust is applied to the bearing unit 111. As a result, the holder carrying rod 12 cannot reciprocate in the sleeve 11 smoothly. In addition, the parts in the sleeve 11 are liable to be damaged.